Stacked vertical transport field effect transistor electrically erasable programmable read only memory (EEPROM) devices

ABSTRACT

A vertically stacked set of an n-type vertical transport field effect transistor (n-type VT FET) and a p-type vertical transport field effect transistor (p-type VT FET) is provided. The vertically stacked set of the n-type VT FET and the p-type VT FET includes a first bottom source/drain layer on a substrate, that has a first conductivity type, a lower channel pillar on the first bottom source/drain layer, and a first top source/drain on the lower channel pillar, that has the first conductivity type. The vertically stacked set of the n-type VT FET and the p-type VT FET further includes a second bottom source/drain on the first top source/drain, that has a second conductivity type different from the first conductivity type, an upper channel pillar on the second bottom source/drain, and a second top source/drain on the upper channel pillar, that has the second conductivity type.

BACKGROUND Technical Field

The present invention generally relates to forming vertical transportfield effect transistors (VT FETs), and more particularly to formingcomplementary metal-oxide-semiconductor devices and electricallyerasable programmable read-only memories (EEPROMs) from VT FETs.

Description of the Related Art

In an electrically erasable programmable read-only memory (EEPROM) a bitof data can be electrically stored and erased using different voltages.A complementary metal-oxide-semiconductor (CMOS) device can form a logicgate. A programmable CMOS device can be formed utilizing a p-type fieldeffect transistor (PFET) and an n-type field effect transistor (NFET)with a common floating gate. The programming, erasure, and/orreprogramming can be effected by placement of a charge into the floatinggate, where the CMOS device can control programming of the floatinggate.

A Field Effect Transistor (FET) typically has a source, a channel, and adrain, where current flows from the source to the drain, and a gate thatcontrols the flow of current through the device channel. Field EffectTransistors (FETs) can have a variety of different structures, forexample, FETs have been fabricated with the source, channel, and drainformed in the substrate material itself, where the current flowshorizontally (i.e., in the plane of the substrate), and FinFETs havebeen formed with the channel extending outward from the substrate, butwhere the current also flows horizontally from a source to a drain. Thechannel for the FinFET can be an upright slab of thin rectangularsilicon (Si), commonly referred to as the fin with a gate on the fin, ascompared to a MOSFET with a single gate parallel with the plane of thesubstrate. Depending on the doping of the source and drain, an NFET or aPFET can be formed.

SUMMARY

In accordance with an embodiment of the present invention, a verticallystacked set of an n-type vertical transport field effect transistor(n-type VT FET) and a p-type vertical transport field effect transistor(p-type VT FET) is provided. The vertically stacked set of the n-type VTFET and the p-type VT FET includes a first bottom source/drain layer ona substrate, wherein the first bottom source/drain layer has a firstconductivity type. The vertically stacked set of the n-type VT FET andthe p-type VT FET further includes a lower channel pillar on the firstbottom source/drain layer, and a first top source/drain on the lowerchannel pillar, wherein the first top source/drain has the firstconductivity type. The vertically stacked set of the n-type VT FET andthe p-type VT FET further includes a second bottom source/drain on thefirst top source/drain, wherein the second bottom source/drain has asecond conductivity type different from the first conductivity type, andan upper channel pillar on the second bottom source/drain, and a secondtop source/drain on the upper channel pillar, wherein the second topsource/drain has the second conductivity type different from the firstconductivity type.

In accordance with another embodiment of the present invention, anelectrically erasable programmable read-only memory (EEPROM) array isprovided. The electrically erasable programmable read-only memory(EEPROM) array includes a plurality of stacked vertical transport fieldeffect transistors (VT FETs), wherein the stacked VT FETs each includean n-type vertical transport field effect transistor and a p-typevertical transport field effect transistor collinear with one another,and a first bit line connected to a source of at least one of the n-typevertical transport field effect transistors. The (EEPROM) array furtherincludes a second bit line connected to a source of at least one of thep-type vertical transport field effect transistors, and a word lineconnected to a common drain of the at least one n-type verticaltransport field effect transistor and the at least one p-type verticaltransport field effect transistor.

In accordance with yet another embodiment of the present invention, amethod of forming a vertically stacked set of an n-type verticaltransport field effect transistor (n-type VT FET) and a p-type verticaltransport field effect transistor (p-type VT FET) is provided. Themethod includes forming a first bottom source/drain layer on asubstrate, wherein the first bottom source/drain layer has a firstconductivity type, forming a lower channel layer on the first bottomsource/drain layer, and forming a first top source/drain layer on thelower channel layer, wherein the first top source/drain layer has thefirst conductivity type. The method further includes forming a secondbottom source/drain layer on the first top source/drain layer, whereinthe second bottom source/drain layer has a second conductivity typedifferent from the first conductivity type, forming an upper channellayer on the second bottom source/drain layer, and forming a second topsource/drain layer on the upper channel layer, wherein the second topsource/drain layer has the second conductivity type different from thefirst conductivity type. The method further includes forming one or morefin templates on the second top source/drain layer, and removing theportions of the second top source/drain layer and the other underlyinglayers not covered by the one or more fin templates down to the firstbottom source/drain layer to form one or more vertically stacked sets ofchannel pillars and source/drains.

These and other features and advantages will become apparent from thefollowing detailed description of illustrative embodiments thereof,which is to be read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The following description will provide details of preferred embodimentswith reference to the following figures wherein:

FIG. 1 is a cross-sectional side view showing a substrate, in accordancewith an embodiment of the present invention;

FIG. 2 is a cross-sectional side view showing a bottom PFET source/drainlayer, a lower channel layer, and a top PFET source/drain layer on thesubstrate, in accordance with an embodiment of the present invention;

FIG. 3 is a cross-sectional side view showing a bottom NFET source/drainlayer on the top PFET source/drain layer, an upper channel layer, and atop NFET source/drain layer, in accordance with an embodiment of thepresent invention;

FIG. 4 is a cross-sectional side view showing a bottom PFET source/drainlayer, a lower channel pillar on the bottom PFET source/drain layer, atop PFET source/drain on the lower channel pillar, a bottom NFETsource/drain on the top PFET source/drain, an upper channel pillar onthe bottom NFET source/drain, a top PFET source/drain on the upperchannel pillar, and a fin template on the top PFET source/drain, inaccordance with an embodiment of the present invention;

FIG. 5 is a cross-sectional side view showing a vertically stacked setof channel pillars and source/drains with a liner on the stack, a bottomspacer layer, a lower dummy gate layer, a first middle spacer layer, agap layer, a second middle spacer layer, an upper dummy gate layer, atop spacer layer, and a cap layer, in accordance with an embodiment ofthe present invention;

FIG. 6 is a cross-sectional side view showing a vertically stacked setof channel pillars and source/drains with a liner on the stack, a bottomspacer, a lower dummy gate plug, a first middle spacer, a middle gapplug, a second middle spacer, an upper dummy gate plug, a top spacer,and a cap plug, in accordance with an embodiment of the presentinvention;

FIG. 7 is a cross-sectional side view showing a vertically stacked setof channel pillars and source/drains with liner segments on the stackafter removing the lower dummy gate plug and upper dummy gate plug, anda gate dielectric layer on the lower channel pillar and upper channelpillar, in accordance with an embodiment of the present invention;

FIG. 8 is a cross-sectional side view showing a vertically stacked setof channel pillars and source/drains with a gate fill layer on the gatedielectric layer, in accordance with an embodiment of the presentinvention;

FIG. 9 is a cross-sectional side view showing a vertically stacked setof channel pillars and source/drains with a lower gate structure on thelower channel pillar, and an upper gate structure on the upper channelpillar, in accordance with an embodiment of the present invention;

FIG. 10 is a cross-sectional side view showing a top PFET source/drain,a bottom NFET source/drain, a top NFET source/drain, and a fin templatepartially exposed after removing the gate mask, middle gap plug, and capplug, in accordance with an embodiment of the present invention;

FIG. 11 is a cross-sectional side view showing a conductive strap on thetop PFET source/drain and bottom NFET source/drain, and a conductivecollar on the top PFET source/drain, in accordance with an embodiment ofthe present invention;

FIG. 12 is a cross-sectional side view showing stacked verticaltransport field effect transistors (VT FETs) of complementarymetal-oxide-semiconductor (CMOS) devices forming an electricallyerasable programmable read-only memory (EEPROM), in accordance with anembodiment of the present invention; and

FIG. 13 is a diagram of an EEPROM array formed by a plurality of stackedvertical transport field effect transistors with common floating gates.

DETAILED DESCRIPTION

Embodiments of the present invention generally relates to formingstacked vertical transport field effect transistors (VT FETs), and moreparticularly to forming complementary metal-oxide-semiconductor (CMOS)devices and electrically erasable programmable read-only memories(EEPROMs) from stacked VT FETs. With the NFET and PFET stacked on top ofeach other, simple wiring of input, output, and power supply lines canbe achieved, thus saving space/foot print area.

Embodiments of the present invention relate to forming a stackedcomplementary metal-oxide-semiconductor (CMOS) device, where an n-typevertical transport field effect transistor (VT NFET) and a p-typevertical transport field effect transistor (VT PFET) are verticallystacked on one another. Vertical stacking of two vertical transportfield effect transistors allows the area occupied by each CMOS device tobe essentially cut in half.

Embodiments of the present invention relate to forming electricallyerasable programmable read only memory (EEPROM) from vertically stackedvertical transport field effect transistors (VT FETs), where thevertical integration of the VT FETs can reduce costs and chipcomplexity. The n-type vertical transport field effect transistor and ap-type vertical transport field effect transistor can have floatinggates to provide read/write functionality. Hot carrier injection can beachieved using Si₃N₄, Y₂O, ZrO₂, or HfO₂ for the floating gatedielectric. Carrier injection for writing to and erasing from thefloating gate can be achieved at a Vds>1.5 V. The gate dielectric of theVT FETs forming the EEPROM can be thicker than the gate dielectric of aVT FET forming a logic device.

Embodiments of the present invention relate to electrically coupling thesource/drains on the n-type vertical transport field effect transistorand a p-type vertical transport field effect transistor to form a commonterminal.

Exemplary applications/uses to which the present invention can beapplied include, but are not limited to: EEPROMS.

It is to be understood that aspects of the present invention will bedescribed in terms of a given illustrative architecture; however, otherarchitectures, structures, substrate materials and process features andsteps can be varied within the scope of aspects of the presentinvention.

Referring now to the drawings in which like numerals represent the sameor similar elements and initially to FIG. 1, a cross-sectional side viewof a substrate is shown, in accordance with an embodiment of the presentinvention.

In one or more embodiments, a substrate 110 can be, for example, asingle crystal semiconductor material wafer or asemiconductor-on-insulator stacked wafer. The substrate can include asupport layer that provides structural support, and an activesemiconductor layer that can form devices. An insulating layer (e.g., aburied oxide (BOX) layer) may be between the active semiconductor layerand the support layer to form a semiconductor-on-insulator substrate(SeOI) (e.g., a silicon-on-insulator substrate (SOI)), or an implantedlayer can form a buried insulating material.

The support layer can include crystalline, semi-crystalline,micro-crystalline, nano-crystalline, and/or amorphous phases. Thesupport layer can be a semiconductor (e.g., silicon (Si), siliconcarbide (Si_(x)C_(y)), silicon-germanium (Si_(x)Gey), germanium (Ge),gallium-arsenide (Ga_(x)As_(y)), cadmium-telluride (Cd_(x)Te_(y)),etc.), an insulator (e.g.: glass (e.g. silica, borosilicate glass),ceramic (e.g., aluminum oxide (Al₂O₃, sapphire), plastic (e.g.,polycarbonate, polyacetonitrile), metal (e.g. aluminum, gold, titanium,molybdenum-copper (Mo_(x)Cu_(y)) composites, etc.), or combinationthereof.

The substrate or active semiconductor layer can be a crystallinesemiconductor, for example, a IV or IV-IV semiconductor (e.g., silicon(Si), silicon-germanium (Si_(x)Ge_(y)), germanium (Ge)), a III-Vsemiconductor (e.g., gallium-arsenide (Ga_(x)As_(y)),indium-gallium-arsenide (In_(x)Ga_(y)As_(x)), indium-phosphide(In_(x)P_(y)), indium-antimonide (In_(x)Sb_(y))), a II-VI semiconductor(e.g., cadmium-telluride (Cd_(x)Te_(y)), zinc-telluride (Zn_(x)Te_(y)),zinc sulfide (ZnS_(x)), zinc selenide (Zn_(x)Se_(y))), or a IV-VIsemiconductor (e.g., tin sulfide (SnS_(x)), lead selenide(Pb_(x)Sb_(y))).

FIG. 2 is a cross-sectional side view showing a bottom PFET source/drainlayer, a lower channel layer, and a top PFET source/drain layer on thesubstrate, in accordance with an embodiment of the present invention.

In one or more embodiments, a bottom PFET source/drain layer 120 can beformed on the substrate 110, where the bottom PFET source/drain layer120 can be formed by epitaxial or heteroepitaxial growth on thesubstrate 110, for example, by reduced pressure chemical vapordeposition (RPCVD), rapid thermal chemical vapor deposition (RTCVD), lowpressure CVD (LPCVD), atmospheric pressure chemical vapor deposition(APCVD), molecular beam epitaxy (MBE), vapor phase epitaxy (VPE) orliquid phase epitaxy (LPE), low-energy plasma deposition (LEPD),ultra-high vacuum chemical vapor deposition (UHVCVD), or metal-organicCVD (MOCVD). The bottom PFET source/drain layer 120 can have the samecrystal structure and orientation as the underlying substrate 110.

In one or more embodiments, the bottom PFET source/drain layer 120 canbe made of a semiconductor material, including, but not limited to,silicon (Si), silicon-germanium (Si_(x)Ge_(y)), indium-gallium-arsenide(In_(x)Ga_(y)As_(z)), or indium-phosphide (In_(x)P_(y)).

In various embodiments, the bottom source/drain layer 120 can be dopedusing suitable doping techniques, including but not limited to, ionimplantation, gas phase doping, plasma doping, plasma immersion ionimplantation, cluster doping, infusion doping, liquid phase doping,solid phase doping, etc. Doping can be by in-situ doping (where dopingand epitaxy growth are performed at the same time), and/or ex-situdoping (where doping occurs before and/or after epitaxy). The dopantscan be p-type (e.g., boron (B), aluminum (Al), gallium (Ga), indium(In), for Si or silicon-germanium (Si_(x)Ge_(y)), and Si, Ge, or tin(Sn) for indium-gallium-arsenide (In_(x)Ga_(y)As_(z)), orindium-phosphide (In_(x)P_(y))).

In various embodiments, the doping sequence can be reversed, and thedopants can be n-type (e.g., phosphorus (P), arsenic (As), antimony (Sb)for Si or Si_(x)Ge_(y), and selenium (Se) or tellurium (Te) forIn_(x)Ga_(y)As_(z) or In_(x)P_(y)) to form NFETs.

In one or more embodiments, the bottom PFET source/drain layer 120 canhave a thickness in the range of about 20 nanometers (nm) to about 100nm, or in the range of about 30 nm to about 50 nm, although otherthicknesses are also contemplated.

In one or more embodiments, a lower channel layer 130 can be formed onthe bottom PFET source/drain layer 120, where the lower channel layer130 can be formed by epitaxial or heteroepitaxial growth on thesubstrate 110. The lower channel layer 130 can have the same crystalstructure and orientation as the underlying bottom PFET source/drainlayer 120.

In one or more embodiments, the lower channel layer 130 can be made of asemiconductor material, including, but not limited to, intrinsic silicon(Si), silicon-germanium (Si_(x)Ge_(y)), carbon-doped silicon (Si:C), orindium-gallium-arsenide (In_(x)Ga_(y)As_(z)). In various embodiments,the lower channel layer 130 can be undoped.

In one or more embodiments, the lower channel layer 130 can have athickness in the range of about 10 nm to about 50 nm, or in the range ofabout 15 nm to about 30 nm, although other thicknesses are alsocontemplated. The thickness of the lower channel layer 130 can determinethe height of a subsequently formed lower channel pillar.

In one or more embodiments, a top PFET source/drain layer 140 can beformed on the lower channel layer 130, where the top PFET source/drainlayer 140 can be formed by epitaxial or heteroepitaxial growth. The topPFET source/drain layer 140 can have the same crystal structure andorientation as the underlying lower channel layer 130.

In one or more embodiments, the top PFET source/drain layer 140 can bemade of a semiconductor material, including, but not limited to, silicon(Si), silicon-germanium (Si_(x)Ge_(y)), or indium-gallium-arsenide(In_(x)Ga_(y)As_(z)), or indium-phosphide (In_(x)P_(y)). In variousembodiments, the top PFET source/drain layer 140 can be p-doped.

In various embodiments, the top PFET source/drain layer 140 can be dopedby in-situ doping (where doping and epitaxy growth are performed at thesame time). In-situ doping can be utilized with the epitaxial growth tomaintain sharp junctions and interfaces. The dopants can be p-type(e.g., boron (B), aluminum (Al), gallium (Ga), indium (In), for Si orSi_(x)Ge_(y), and magnesium (Mg) or zinc (Zn) for In_(x)Ga_(y)As_(z))).In various embodiments, the doping sequence can be reversed, and thedopants can be n-type.

In one or more embodiments, the top PFET source/drain layer 140 can havea thickness in the range of about 10 nm to about 100 nm, or in the rangeof about 30 nm to about 60 nm, although other thicknesses are alsocontemplated.

FIG. 3 is a cross-sectional side view showing a bottom NFET source/drainlayer on the top PFET source/drain layer, an upper channel layer, and atop NFET source/drain layer, in accordance with an embodiment of thepresent invention.

In one or more embodiments, a bottom NFET source/drain layer 150 can beformed on the top PFET source/drain layer 140, where the bottom NFETsource/drain layer 150 can be formed by epitaxial or heteroepitaxialgrowth on the top PFET source/drain layer 140. The bottom NFETsource/drain layer 150 can have the same crystal structure andorientation as the underlying top PFET source/drain layer 140.

In one or more embodiments, the bottom NFET source/drain layer 150 canbe made of a semiconductor material, including, but not limited to,silicon (Si), carbon-doped silicon (Si:C), indium-gallium-arsenide(In_(x)Ga_(y)As_(z)), or indium-phosphide (In_(x)P_(y)).

In various embodiments, the bottom NFET source/drain layer 150 can bedoped by in-situ doping (where doping and epitaxy growth are performedat the same time). The dopants can be n-type (e.g., phosphorus, arsenic,antimony for Si or Si_(x)Ge_(y), and Se or Te for In_(x)Ga_(y)As_(z) orIn_(x)P_(y)).

In various embodiments, the doping sequence can be reversed, and thedopants can be p-type (e.g., B, Al, Ga, In, for Si or Si_(x)Ge_(y), andMg or Zn for In_(x)Ga_(y)As_(z) or In_(x)P_(y)).

In one or more embodiments, the bottom NFET source/drain layer 150 canhave a thickness in the range of about 10 nm to about 100 nm, or in therange of about 30 nm to about 60 nm, although other thicknesses are alsocontemplated.

In one or more embodiments, an upper channel layer 160 can be formed onthe bottom NFET source/drain layer 150, where the upper channel layer160 can be formed by epitaxial or heteroepitaxial growth on the bottomNFET source/drain layer 150. The upper channel layer 160 can have thesame crystal structure and same orientation as the underlying bottomNFET source/drain layer 150.

In one or more embodiments, the upper channel layer 160 can be made of asemiconductor material, including, but not limited to, silicon (Si),silicon-germanium (Si_(x)Ge_(y)), carbon-doped silicon (Si:C), orindium-gallium-arsenide (In_(x)Ga_(y)As_(z)). The upper channel layer160 can be a different semiconductor material than the lower channellayer 130. In various embodiments, the upper channel layer 160 can beundoped.

In one or more embodiments, the upper channel layer 160 can have athickness in the range of about 10 nm to about 50 nm, or in the range ofabout 15 nm to about 30 nm, although other thicknesses are alsocontemplated. The thickness of the upper channel layer 160 can determinethe height of a subsequently formed upper channel pillar.

In one or more embodiments, a top NFET source/drain layer 170 can beformed on the upper channel layer 160, where the top NFET source/drainlayer 170 can be formed by epitaxial or heteroepitaxial growth on theupper channel layer 160. The top NFET source/drain layer 170 can havethe same crystal structure and orientation as the underlying upperchannel layer 160.

In one or more embodiments, the top NFET source/drain layer 170 can bemade of a semiconductor material, including, but not limited to, silicon(Si), carbon-doped silicon (Si:C), indium-gallium-arsenide(In_(x)Ga_(y)As_(z)), or indium-phosphide (In_(x)P_(y)).

In various embodiments, the top NFET source/drain layer 170 can be dopedby in-situ doping (where doping and epitaxy growth are performed at thesame time). The dopants can be n-type (e.g., phosphorus, arsenic,antimony for Si or Si_(x)Ge_(y), and Se or Te for In_(x)Ga_(y)As_(z) orIn_(x)P_(y)).

In one or more embodiments, the top NFET source/drain layer 170 can havea thickness in the range of about 20 nm to about 100 nm, or in the rangeof about 30 nm to about 60 nm, although other thicknesses are alsocontemplated. The top NFET source/drain layer 170 and the bottom PFETsource/drain layer 120 can be thicker than the top PFET source/drainlayer 140 and the bottom NFET source/drain layer 150 to allow forreduced access resistances and provide easier contacting and increasedcontact area.

In various embodiments, each of the layers 120, 130, 140, 150, 160, 170can be formed by epitaxial growth through varying the layer precursorsand doping gasses with precise time, temperature, and process controls,to form the whole device stack in-situ (i.e., in a single processchamber) using a continuous sequence of processes.

In one or more embodiments, a template layer can be formed on the topNFET source/drain layer 170, where the template layer can be a hardmasklayer, a softmask layer, or a combination thereof. The template layercan be patterned using a lithographic process and resist to form one ormore fin templates 180 on the top NFET source/drain layer 170.

In one or more embodiments, the template layer can be a hard mask layerformed on the top NFET source/drain layer 170, for example, by chemicalvapor deposition (CVD) or plasma enhanced CVD (PECVD). The hard masklayer can be a dielectric material, including, but not limited to,silicon oxide (SiO_(x)), silicon nitride (Si_(x)N_(y)), siliconoxynitride (Si_(x)O_(y)N_(z)), silicon carbonitride (Si_(x)C_(y)N_(z)),silicon boronitride (Si_(x)B_(y)N_(z)), silicon borocarbide(Si_(x)B_(y)C_(z)), silicon boro carbonitride (Si_(w)B_(x)C_(y)N_(z)),or combinations thereof. The hard mask layer 140 can be selectivelyetchable relative to the channel layers and source/drain layers.

While the figures illustrate an embodiment with PFET layers below theNFET layers, this is for illustrative purposes only, and the order ofthe layers, the type of dopants, and the arrangement of the devices canbe revered. Both arrangements of an NFET and PFET are considered withinthe scope of the present invention, and references to NFET and PFET canbe reversed

FIG. 4 is a cross-sectional side view showing a bottom PFET source/drainlayer, a lower channel pillar on the bottom PFET source/drain layer, atop PFET source/drain on the lower channel pillar, a bottom NFETsource/drain on the top PFET source/drain, an upper channel pillar onthe bottom NFET source/drain, a top PFET source/drain on the upperchannel pillar, and a fin template on the top PFET source/drain, inaccordance with an embodiment of the present invention.

In one or more embodiments, a vertically stacked set of channel pillarsand source/drains 111 can be formed on the substrate 110 by maskingportions of the top NFET source/drain layer 170 and underlying layers,and removing the exposed portions of the top NFET source/drain layer 170and the other underlying layers down to the bottom PFET source/drainlayer 120, where a portion of the bottom PFET source/drain layer 120 canremain on the substrate 110 and a bottom PFET source/drain extensionregion 121 can be formed below a lower channel pillar 131.

In various embodiments, the vertically stacked set of channel pillarsand source/drains 111 can include a bottom PFET source/drain extensionregion 121, a lower channel pillar 131 on the bottom PFET source/drainextension region 121, a top PFET source/drain 141 on the lower channelpillar 131, a bottom NFET source/drain 151 on the top PFET source/drain141, an upper channel pillar 161 on the bottom NFET source/drain 151,and a top NFET source/drain 171 on the upper channel pillar 161. A fintemplate 180 can remain on the top NFET source/drain 171 of the stackedset of channel pillars and source/drains 111.

In one or more embodiments, the vertically stacked set of channelpillars and source/drains 111 can have a width in the range of about 4nm to about 20 nm, or in the range of about 6 nm to about 8 nm, althoughother thicknesses are also contemplated.

The total height of the vertically stacked set of channel pillars andsource/drains 111 can be the sum of the thickness of each of the stackedlayers, where the stacked pair of channel pillars 111 can have a totalheight in the range of about 80 nm to about 500 nm, or in the range ofabout 150 nm to about 290 nm, or in the range of about 120 nm to about180 nm, although other thicknesses are also contemplated.

In one or more embodiments, a stacked pair of channel pillars 111 can beformed on the remaining portion of the bottom PFET source/drain layer120 and substrate 110 by a multiple patterning fabrication process, forexample, a sidewall image transfer (SIT) process, a self-aligned doublepatterning (SADP) process, self-aligned triple patterning (SATP)process, or a self-aligned quadruple patterning (SAQP). The stacked pairof channel pillars 111 may be formed by a direct write process or doublepatterning process using, for example, immersion lithography, extremeultraviolet lithography, or x-ray lithography.

FIG. 5 is a cross-sectional side view showing a vertically stacked setof channel pillars and source/drains with a liner on the stack, a bottomspacer layer, a lower dummy gate layer, a first middle spacer layer, agap layer, a second middle spacer layer, an upper dummy gate layer, atop spacer layer, and a cap layer, in accordance with an embodiment ofthe present invention.

In one or more embodiments, a liner 185 can be formed on the stackedpair of channel pillars 111, and exposed surface of the bottom PFETsource/drain layer 120, where the liner 185 can be formed by a conformaldeposition, for example, atomic layer deposition (ALD) or plasmaenhanced ALD (PEALD), or by a low temperature oxidation.

In one or more embodiments, the liner 185 can be made of a dielectricmaterial, including, but not limited to, silicon oxide (SiO_(x)),silicon nitride (Si_(x)N_(y)), silicon oxynitride (Si_(x)O_(y)N_(z)),silicon carbonitride (Si_(x)C_(y)N_(z)), silicon boronitride(Si_(x)B_(y)N_(z)), silicon borocarbide (Si_(x)B_(y)C_(z)), silicon borocarbonitride (Si_(w)B_(x)C_(y)N_(z)), or combinations thereof. The liner185 can be selectively etchable relative to the fin template 180,channel pillars 131, 161, and source/drains 141, 151, 171.

In various embodiments, the liner 185 can have a thickness in the rangeof about 2 nm to about 10 nm, or in the range of about 3 nm to about 5nm, although other thicknesses are also contemplated.

In one or more embodiments, a bottom spacer layer 190 can be formed onthe liner 185, where the bottom spacer layer 190 can be formed by adirectional deposition, for example, a gas cluster ion beam deposition(GCIB) or high density plasma deposition (HDP). The bottom spacer layer190 can also be formed by a blanket deposition (e.g., CVD, PECVD,spin-on) and etched back to an intended thickness, for example, usingreactive ion etching (RIE) or a wet chemical etch.

In one or more embodiments, the bottom spacer layer 190 can be made of adielectric material, including, but not limited to, silicon oxide(SiO_(x)), silicon nitride (Si_(x)N_(y)), silicon oxynitride(Si_(x)O_(y)N_(z)), silicon carbonitride (Si_(x)C_(y)N_(z)), siliconboronitride (Si_(x)B_(y)N_(z)), silicon borocarbide (Si_(x)B_(y)C_(z)),silicon borocarbonitride (Si_(w)B_(x)C_(y)N_(z)), or combinationsthereof. The bottom spacer layer 190 can be selectively etchablerelative to the liner 185, fin template 180, channel pillars 131, 161,and source/drains 141, 151, 171.

In various embodiments, the bottom spacer layer 190 can have a thicknessin the range of about 4 nm to about 20 nm, or in the range of about 6 nmto about 12 nm, although other thicknesses are also contemplated.

In one or more embodiments, a lower dummy gate layer 200 can be formedon the liner 185 and bottom spacer layer 190, where the lower dummy gatelayer 200 can be formed by a directional deposition, for example, a gascluster ion beam deposition (GCIB) or high density plasma deposition(HDP). The lower dummy gate layer 200 can also be formed by a blanketdeposition (e.g., CVD, PECVD, spin-on) and etched back to an intendedthickness, for example, using reactive ion etching (RIE) or a wetchemical etch.

In one or more embodiments, the lower dummy gate layer 200 can be madeof a semiconductor material, for example, amorphous silicon (a-Si), aninsulator, for example, a spin-on glass, or an amorphous carbon (a-C),or combinations thereof. The lower dummy gate layer 200 can beselectively etchable relative to the liner 185 and bottom spacer layer190.

In various embodiments, the lower dummy gate layer 200 can have athickness in the range of about 10 nm to about 50 nm, or in the range ofabout 15 nm to about 30 nm, although other thicknesses are alsocontemplated. The lower dummy gate layer 200 can have a thickness lessthan or equal to the thickness of the lower channel pillar 131, wherethe top surface of the lower dummy gate layer can be coplanar with orbelow the bottom surface of the top PFET source/drain 141, and thebottom surface of the lower dummy gate layer can be coplanar with orabove the top surface of bottom PFET source/drain extension region 121.

In one or more embodiments, a first middle spacer layer 210 can beformed on the lower dummy gate layer 200 and liner 185, where the firstmiddle spacer layer 210 can be formed by a directional deposition, forexample, a gas cluster ion beam deposition (GCIB) or high density plasmadeposition (HDP). The first middle spacer layer 210 can also be formedby a blanket deposition (e.g., CVD, PECVD, spin-on) and etched back toan intended thickness, for example, using reactive ion etching (RIE) ora wet chemical etch.

In one or more embodiments, the first middle spacer layer 210 can bemade of a dielectric material (e.g., silicon oxide (SiO_(x)), siliconnitride (Si_(x)N_(y)), silicon oxynitride (Si_(x)O_(y)N_(z)), siliconcarbonitride (Si_(x)C_(y)N_(z)), silicon boronitride (Si_(x)B_(y)N_(z)),silicon borocarbide (Si_(x)B_(y)C_(z)), silicon borocarbonitride(Si_(w)B_(x)C_(y)N_(z)), or combinations thereof). The first middlespacer layer 210 can be selectively etchable relative to the liner 185and lower dummy gate layer 200.

In various embodiments, the first middle spacer layer 210 can have athickness in the range of about 4 nm to about 20 nm, or in the range ofabout 6 nm to about 12 nm, although other thicknesses are alsocontemplated.

In one or more embodiments, a gap layer 220 can be formed on the firstmiddle spacer layer 210 and liner 185, where the gap layer 220 can beformed by a directional deposition, for example, a gas cluster ion beamdeposition (GCIB) or high density plasma deposition (HDP). The gap layer220 can also be formed by a blanket deposition (e.g., CVD, PECVD,spin-on) and etched back to an intended thickness, for example, usingreactive ion etching (RIE) or a wet chemical etch.

In one or more embodiments, a gap layer 220 can be made of a dielectricmaterial (e.g., SiO_(x), Si_(x)N_(y), Si_(x)O_(y)N_(z),Si_(x)C_(y)N_(z), Si_(x)B_(y)N_(z), Si_(x)B_(y)C_(z),Si_(w)B_(x)C_(y)N_(z), or combinations thereof). The gap layer 220 canbe selectively etchable relative to the liner 185 and first middlespacer layer 210.

In various embodiments, the gap layer 220 can have a thickness in therange of about 40 nm to about 200 nm, or in the range of about 50 nm toabout 120 nm, although other thicknesses are also contemplated.

In one or more embodiments, a second middle spacer layer 230 can beformed on the gap layer 220 and liner 185, where the second middlespacer layer 230 can be formed by a directional deposition (e.g., GCIB,HDP). The second middle spacer layer 230 can also be formed by a blanketdeposition (e.g., CVD, PECVD, spin-on) and etched back to an intendedthickness, for example, using reactive ion etching (RIE) or a wetchemical etch.

In one or more embodiments, the second middle spacer layer 230 can bemade of a dielectric material, including, but not limited to, SiO_(x),Si_(x)N_(y), Si_(x)O_(y)N_(z), Si_(x)C_(y)N_(z), Si_(x)B_(y)N_(z),Si_(x)B_(y)C_(z), Si_(w)B_(x)C_(y)N_(z), or combinations thereof. Thesecond middle spacer layer 230 can be selectively etchable relative tothe liner 185 and gap layer 220.

In various embodiments, the second middle spacer layer 230 can have athickness in the range of about 4 nm to about 20 nm, or in the range ofabout 6 nm to about 12 nm, although other thicknesses are alsocontemplated.

In a non-limiting exemplary embodiment, the first middle spacer layer210 can be a dielectric nitride (e.g., Si_(x)N_(y)), the gap layer 220can be a dielectric oxide (e.g., SiO_(x)), and the second middle spacerlayer 230 can be a dielectric nitride (e.g., Si_(x)N_(y)).

In one or more embodiments, an upper dummy gate layer 240 can be formedon the liner 185 and second middle spacer layer 230, where the upperdummy gate layer 240 can be formed by a directional deposition (e.g.,GCIB or HDP). The upper dummy gate layer 240 can also be formed by ablanket deposition (e.g., CVD, PECVD, spin-on) and etched back to anintended thickness, for example, using reactive ion etching (RIE) or awet chemical etch.

In one or more embodiments, the upper dummy gate layer 240 can be madeof a semiconductor material, for example, amorphous silicon (a-Si), aninsulator, for example, a spin-on glass, or an amorphous carbon (a-C),or combinations thereof. The upper dummy gate layer 240 can beselectively etchable relative to the liner 185 and second middle spacerlayer 230.

In various embodiments, the upper dummy gate layer 240 can have athickness in the range of about 10 nm to about 50 nm, or in the range ofabout 15 nm to about 30 nm, although other thicknesses are alsocontemplated. The upper dummy gate layer 240 can have a thickness lessthan or equal to the thickness of the upper channel pillar 161, wherethe top surface of the upper dummy gate layer 240 can be coplanar withor below the bottom surface of the top NFET source/drain 171, and thebottom surface of the upper dummy gate layer can be coplanar with orabove the top surface of bottom NFET source/drain 151.

In one or more embodiments, a top spacer layer 250 can be formed on theupper dummy gate layer 240 and liner 185, where the top spacer layer 250can be formed by a directional deposition, for example, a gas clusterion beam deposition (GCIB) or high density plasma deposition (HDP). Thetop spacer layer 250 can also be formed by a blanket deposition (e.g.,CVD, PECVD, spin-on) and etched back to an intended thickness, forexample, using reactive ion etching (RIE) or a wet chemical etch.

In one or more embodiments, the top spacer layer 250 can be made of adielectric material, including, but not limited to, SiO_(x),Si_(x)N_(y), Si_(x)O_(y)N_(z), Si_(x)C_(y)N_(z), Si_(x)B_(y)N_(z),Si_(x)B_(y)C_(z), Si_(w)B_(x)C_(y)N_(z), or combinations thereof. Thetop spacer layer 250 can be selectively etchable relative to the liner185 and upper dummy gate layer 240.

In various embodiments, the top spacer layer 250 can have a thickness inthe range of about 4 nm to about 20 nm, or in the range of about 6 nm toabout 12 nm, although other thicknesses are also contemplated.

In one or more embodiments, a cap layer 260 can be formed on the topspacer layer 250 and liner 185, where the cap layer 260 can be formed bya directional deposition (e.g., GCIB, HDP). The cap layer 260 can alsobe formed by a blanket deposition (e.g., CVD, PECVD, spin-on) and etchedback to an intended thickness, for example, using reactive ion etching(RIE) or a wet chemical etch.

In one or more embodiments, a cap layer 260 can be made of a dielectricmaterial (e.g., SiO_(x), Si_(x)N_(y), Si_(x)O_(y)N_(z),Si_(x)C_(y)N_(z), Si_(x)B_(y)N_(z), Si_(x)B_(y)C_(z),Si_(w)B_(x)C_(y)N_(z), or combinations thereof). The cap layer 260 canbe selectively etchable relative to the liner 185 and top spacer layer250.

In various embodiments, the cap layer 260 can have a thickness in therange of about 30 nm to about 250 nm, or in the range of about 50 nm toabout 150 nm, although other thicknesses are also contemplated.

In various embodiments, a portion of the cap layer 260 extending abovethe liner 185 and fin template 180 can be removed usingchemical-mechanical polishing (CMP) to provide a smooth, flat surface,where the portion of the liner 185 on the top surface of the fintemplate 180 can also be removed to expose the fin template. The caplayer 260 can cover the underlying structure and provide a referencesurface for subsequent processing.

FIG. 6 is a cross-sectional side view showing a vertically stacked setof channel pillars and source/drains with a liner on the stack, a bottomspacer, a lower dummy gate plug, a first middle spacer, a middle gapplug, a second middle spacer, an upper dummy gate plug, a top spacer,and a cap plug, in accordance with an embodiment of the presentinvention.

In one or more embodiments, a gate mask 270 can be formed on the fintemplate 180, cap layer 260, and underlying layers, where the gate mask270 can be a hardmask, including, but not limited to, silicon oxide(SiO_(x)), silicon nitride (Si_(x)N_(y)), silicon oxynitride(Si_(x)O_(y)N_(z)), silicon carbonitride (Si_(x)C_(y)N_(z)), siliconboronitride (Si_(x)B_(y)N_(z)), silicon borocarbide (Si_(x)B_(y)C_(z)),silicon borocarbonitride (Si_(w)B_(x)C_(y)N_(z)), or combinationsthereof. The gate mask 270 can protect the underlying material layersduring removal of portions of the dummy gate layers, spacer layers, anda later formed gate fill layer that extend laterally beyond the gatemask 270.

In one or more embodiments, a directional etch (e.g., RIE) can be usedto remove the exposed portions of the bottom spacer layer 190, lowerdummy gate layer 200, first middle spacer layer 210, gap layer 220,second middle spacer layer 230, upper dummy gate layer 240, top spacerlayer 250, and cap layer 260 to form a bottom spacer 192, a lower dummygate plug 202, a first middle spacer 212, a middle gap plug 222, asecond middle spacer 232, an upper dummy gate plug 242, a top spacer252, and a cap plug 262 on the liner 185 and sidewalls of the stackedpair of channel pillars 111.

In various embodiments, a portion of the liner 185 can be removed fromthe surface of the bottom PFET source/drain layer 120 to form linersegments below the bottom spacer 192.

FIG. 7 is a cross-sectional side view showing a vertically stacked setof channel pillars and source/drains with liner segments on the stackafter removing the lower dummy gate plug and upper dummy gate plug, anda gate dielectric layer on the lower channel pillar and upper channelpillar, in accordance with an embodiment of the present invention.

In one or more embodiments, the lower dummy gate plug 202 and upperdummy gate plug 242 can be removed, where the lower dummy gate plug 202and upper dummy gate plug 242 can be removed using an isotropic etch,for example, a wet chemical etch or dry plasma etch. Removing the lowerdummy gate plug 202 and upper dummy gate plug 242 can expose portions ofthe liner 185 on the lower channel pillar 131 and upper channel pillar161. In various embodiments, the exposed portions of the liner 185 canbe removed to expose the sidewalls of the lower channel pillar 131 andupper channel pillar 161. Liner segments 187 can remain on portions ofthe bottom NFET source/drain 151 and the top PFET source/drain 141, andon portions of the top NFET source/drain 171 and fin template 180.

In one or more embodiments, a gate dielectric layer 280 can be formed onthe exposed portions of the lower channel pillar 131 and upper channelpillar 161, and other exposed surfaces, where the gate dielectric layer280 can be formed by conformal depositions (e.g., ALD, PEALD).

In one or more embodiments, a gate dielectric layer 280 can be siliconoxide (SiO_(x)), silicon nitride (Si_(x)N_(y)), silicon oxynitride(Si_(x)O_(y)N_(z)), boron nitride (BN), high-k dielectric materials, ora combination thereof. Examples of high-k materials include but are notlimited to metal oxides, such as, hafnium oxide (HfO_(x)), hafniumsilicon oxide (Hf_(x)Si_(y)O_(z)), hafnium silicon oxynitride(Hf_(w)Si_(x)O_(y)N_(z)), lanthanum oxide (LaO_(x)), lanthanum aluminumoxide (La_(x)Al_(y)O_(z)), zirconium oxide (ZrO_(x)), zirconium siliconoxide (Zr_(x)Si_(y)O_(z)), zirconium silicon oxynitride(Zr_(w)Si_(x)O_(y)N_(z)), tantalum oxide (TaO_(x)), titanium oxide(TiO_(x)), barium strontium titanium oxide (Ba_(w)Sr_(x)Ti_(y)O_(z)),barium titanium oxide (Ba_(x)Ti_(y)O_(z)), strontium titanium oxide(Sr_(x)Ti_(y)O_(z)), yttrium oxide (Y_(x)O_(y)), aluminum oxide(Al_(x)O_(y)), lead scandium tantalum oxide (Pb_(w)Sc_(x)Ta_(y)O_(z)),and lead zinc niobate (Pb_(w)Zn_(x)Nb_(y)O_(z)). The high-k material mayfurther include dopants such as lanthanum, aluminum, magnesium, orcombinations thereof.

In various embodiments, the gate dielectric layer 280 can have athickness in the range of about 10 nm to about 50 nm, or about 15 nm toabout 40 nm, or about 20 nm to about 30 nm, although other thicknessesare contemplated. The gate dielectric layer 280 can have a thicknesssufficient to maintain an electrical charge above a minimum value for apredetermined period of time based on the rate of charge loss throughtunneling.

FIG. 8 is a cross-sectional side view showing a vertically stacked setof channel pillars and source/drains with a gate fill layer on the gatedielectric layer, in accordance with an embodiment of the presentinvention.

In one or more embodiments, a gate fill layer 300 can be formed on thegate dielectric layer 280, where the gate fill layer 300 can be formedby a conformal deposition (e.g., ALD, PEALD), CVD, PECVD, MOCVD,physical vapor deposition (PVD), or a combination thereof. A CMP can beused to remove excess gate fill layer 300, and provide a smooth, flatsurface.

The gate fill layer 300 can be made of a conductive material, which canbe polysilicon (p-Si), a metal, for example, tungsten (W), copper (Cu),cobalt (Co), tantalum (Ta), titanium (Ti), manganese (Mn); a conductivemetal compound, for example, tantalum nitride (TaN), titanium nitride(TiN), titanium carbide (TiC), a copper manganese alloy (Cu—Mn), or anysuitable combination thereof.

FIG. 9 is a cross-sectional side view showing a vertically stacked setof channel pillars and source/drains with a lower gate structure on thelower channel pillar, and an upper gate structure on the upper channelpillar, in accordance with an embodiment of the present invention.

In one or more embodiments, a portion of the gate fill layer 300 notcovered by the top spacer 252, cap plug 262, and gate mask 270 can beremoved, where the portion of the gate fill layer 300 in the recessedareas under the top spacer 252 and a cap plug 262 can remain to form anupper gate electrode 304 of an upper gate structure for an NFET. Theportion of the gate fill layer 300 in the recessed areas under the firstmiddle spacer 212, middle gap plug 222, and second middle spacer 232 canremain to form a lower gate electrode 302 of lower gate structure for aPFET. The portion of the gate fill layer 300 not covered by the cap plug262 can be removed using a directional etch (e.g., RIE).

In one or more embodiments, an upper portion of the bottom PFETsource/drain layer 120 can be partially removed during removal of thegate fill layer 300 and gate dielectric layer 280.

In one or more embodiments, the exposed portions of the gate dielectriclayer 280 can be removed from the cap plug 262, top spacer 252, firstmiddle spacer 212, middle gap plug 222, second middle spacer 232, andbottom spacer 192 during removal of portions of the gate fill layer 300.The gate dielectric layer 280 can also be removed from the bottom PFETsource/drain layer 120. A portion of the gate dielectric layer 280 canremain on the bottom spacer 192, lower channel pillar 131, and firstmiddle spacer 212 forming a lower gate structure dielectric layer 282 onthe lower channel pillar 131. A portion of the gate dielectric layer 280can remain on the second middle spacer 232, upper channel pillar 161,and top spacer 252 forming an upper gate structure dielectric layer 284on the upper channel pillar 161.

In a non-limiting exemplary embodiment, the lower gate structuredielectric layer 282 and upper gate structure dielectric layer 284 canbe silicon nitride (Si_(x)N_(y)) (e.g., Si₃N₄), yttrium oxide(Y_(x)O_(y)) (e.g., Y₂O₃), zirconium oxide (ZrO_(x)) (e.g., ZrO₂), orhafnium oxide (HfO_(x)) (e.g., HfO₂).

In various embodiments, removal of portions of the gate dielectric layer280 can expose the cap plug 262 and middle gap plug 222.

FIG. 10 is a cross-sectional side view showing a top PFET source/drain,a bottom NFET source/drain, a top NFET source/drain, and a fin templatepartially exposed after removing the gate mask, middle gap plug, and capplug, in accordance with an embodiment of the present invention.

In one or more embodiments, the cap plug 262 and middle gap plug 222 canbe removed using an isotropic etch to expose the underlying portions ofthe liner segments 187. In various embodiments, portions of the linersegments 187 exposed by removal of the cap plug 262 and middle gap plug222 can be removed using an isotropic etch to expose at least a portionof the top PFET source/drain 141 on the lower channel pillar 131, atleast a portion of the bottom NFET source/drain 151 on the top PFETsource/drain 141, and at least a portion of the top NFET source/drain171 on the upper channel pillar 161. In various embodiments, theinterface between the bottom NFET source/drain 151 and the top PFETsource/drain 141 can be exposed.

Portions of the liner segments 187 covered by the bottom spacer 192,first middle spacer 212, second middle spacer 232, and top spacer 252can remain as separation bands 188 on a portion of the bottom NFETsource/drain 151, the top PFET source/drain 141, and the top NFETsource/drain 171.

FIG. 11 is a cross-sectional side view showing a conductive strap on thetop PFET source/drain and bottom NFET source/drain, and a conductivecollar on the top PFET source/drain, in accordance with an embodiment ofthe present invention.

In one or more embodiments, a conductive strap 312 can be formed on thetop PFET source/drain 141 and bottom NFET source/drain 151, where theconductive strap 312 can be formed by a self-aligned silicide process,where a metal forming the silicide can be conformally and/or selectivelydeposited (e.g., ALD) on the top PFET source/drain 141 and bottom NFETsource/drain 151, and reacted with silicon to form a silicide. Theconductive strap 312 can form a conductive path between the top PFETsource/drain 141 and bottom NFET source/drain 151, where the conductivestrap 312 can form an electrical connection to a common drain contact ofthe vertically stacked set 111.

In one or more embodiments, the conductive strap 312 can be made of aconductive silicide material, which can be tungsten silicide (WSi_(x)),titanium silicide (TiSi_(x)), cobalt silicide (CoSi_(x)), molybdenumsilicide (MoSi_(x)), and nickel silicide (NiSi_(x)), or suitablecombinations thereof.

In one or more embodiments, the conductive strap 312 can have athickness in the range of about 6 nm to about 20 nm, or in the range ofabout 8 nm to about 12 nm, although other thicknesses are alsocontemplated. The conductive strap 312 can electrically couple thebottom NFET source/drain 151 to the top PFET source/drain 141 to providea conductive path around the P-N junction (diode interface).

In various embodiments, the conductive strap 312 can be electricallyconnected to a common source/drain connection for the CMOS device. Theconductive strap 312 can also provide an electrical connection to ametal line.

In one or more embodiments, a conductive collar 314 can be formed on thetop NFET source/drain 171, where the conductive collar 314 can be formedby the same self-aligned silicide process as the conductive strap 312.

In various embodiments, the conductive collar 314 an be conductivesilicide material (e.g., WSi_(x), TiSi_(x), CoSi_(x), MoSi_(x), andNiSi_(x)), or any suitable combination thereof. The conducting silicidematerial can protect the portion of the top NFET source/drain 171 abovethe top spacer 252 during subsequent processing.

In one or more embodiments, the conductive collar 314 can have athickness in the range of about 6 nm to about 20 nm, or in the range ofabout 8 nm to about 12 nm, although other thicknesses are alsocontemplated.

FIG. 12 is a cross-sectional side view showing stacked verticaltransport field effect transistors (VT FETs) of a complementarymetal-oxide-semiconductor devices forming an electrically erasableprogrammable read-only memory (EEPROM), in accordance with an embodimentof the present invention.

In one or more embodiments, an interlayer dielectric (ILD) layer 330 canbe formed on the gate structures, including the lower gate electrode 302and lower gate structure dielectric layer 282 on the lower channelpillar 131, and the upper gate electrode 304 and upper gate structuredielectric layer 284 on the upper channel pillar 161. The interlayerdielectric (ILD) layer 330 can be formed by a blanket deposition, wherethe ILD layer can fill in the recesses between the first middle spacer212 and second middle spacer 232 adjacent to the conductive strap 312.

In one or more embodiments, the interlayer dielectric (ILD) layer 330can be made of silicon oxide (SiO_(x)) (e.g., SiO₂), a low-K material,or a combination thereof. A low-K dielectric can include amorphouscarbon (a-C), fluorine doped silicon oxide (SiO_(x):F), carbon dopedsilicon oxide (SiO_(x):C), Si_(x)C_(y)O_(z)H, silicon borocarbonitride(Si_(w)B_(x)C_(y)N_(z)), or a combination thereof.

In one or more embodiments, electrical contacts 340, 350, 360, can beformed to the bottom PFET source/drain layer 120, top NFET source/drain171, lower gate electrode 302 and common upper gate electrode 304. Thecommon electrical contact 360 formed to the lower gate electrode 302 andupper gate electrode 304 can provide a floating electrical connectionbetween the lower gate electrode 302 and upper gate electrode 304, wherethe common electrical contact 360 is not electrically connected to avoltage source, current source, or ground.

FIG. 13 is a diagram of an EEPROM Array formed by a plurality of stackedvertical transport field effect transistors with common floating gates.

In one or more embodiments, a plurality of stacked vertical transportfield effect transistors (VT FETs) 521, 522, 523 can form an EEPROMarray 500, where the stacked VT FETs can include an n-type verticaltransport field effect transistor and a p-type vertical transport fieldeffect transistor collinear with one another.

The EEPROM array 500 can include a plurality of bit lines 501, 502, 503,504, and word lines 511, 512, 513, with one access transistor 541, 542,543 per wordline, WL0, WL1, WL2. A conductive strap 312 can form anelectrical connection to a common drain contact 533 of a stackedvertical transport field effect transistor (VT FET) 523. The commonelectrical contact 360 can electrically connect the lower gate electrode302 with the upper gate electrode 304.

EEPROM cells and memory arrays employing common-floating-gateparallel-nFET-pFET devices can have efficient avalanche hot-electroninjection in PFET 557 and efficient avalanche hot-hole injection in theNFET 567. The parallel-nFET-pFET devices can be programmed throughavalanche hot-electron injection into the floating gate through the PFET557 to place a negative voltage on the floating gate. Theparallel-nFET-pFET devices can be erased through avalanche hot-holeinjection into the floating gate through the NFET 567 to remove thenegative charge and/or place a positive voltage on the floating gate. Anegative charge accumulated on the floating gate can be sufficient toturn off the conduction of an enhancement mode NFET 567. A positivecharge accumulated on the floating gate can be sufficient to turn offthe conduction of a PFET 557. The charge injection and removal can bedetermined by the voltage drop between the drain and gate terminals. Invarious embodiments, a memory cell can utilize enhancement mode NFET 567and PFET 557 devices, where the memory cell can be programmed byavalanche hot-electron injection and avalanche hot-hole injection.

In operation, the common floating gate connected by electrical contact360 can be programmed by avalanche hot-electron injection from the PFETto write a “1”, and avalanche hot-hole injection from the NFET to writea “0”. The voltage difference between bitline B0L and bitline B0R isdivided between NFET and PFET, such that Vds across either NFET or PFETis not large enough to cause hot-carrier injection. In writing a “1”,Vds=−3.0 V across the floating-gate pFET, causing hot-electron injectioninto the pFET. For example, for stacked vertical transport field effecttransistor (VT FET) 523 a WL0 voltage of 1.5 V and −3 V on B0R can writea “1” to the PFET.

In writing a “0”, Vds=3.0 V across the nFET, causing hot-hole injectionin the NFET.

In reading the NFET, Vds=1.5 V across both the NFET and the PFET.

The present embodiments can include a design for an integrated circuitchip, which can be created in a graphical computer programming language,and stored in a computer storage medium (such as a disk, tape, physicalhard drive, or virtual hard drive such as in a storage access network).If the designer does not fabricate chips or the photolithographic masksused to fabricate chips, the designer can transmit the resulting designby physical means (e.g., by providing a copy of the storage mediumstoring the design) or electronically (e.g., through the Internet) tosuch entities, directly or indirectly. The stored design is thenconverted into the appropriate format (e.g., GDSII) for the fabricationof photolithographic masks, which typically include multiple copies ofthe chip design in question that are to be formed on a wafer. Thephotolithographic masks are utilized to define areas of the wafer(and/or the layers thereon) to be etched or otherwise processed.

Methods as described herein can be used in the fabrication of integratedcircuit chips. The resulting integrated circuit chips can be distributedby the fabricator in raw wafer form (that is, as a single wafer that hasmultiple unpackaged chips), as a bare die, or in a packaged form. In thelatter case, the chip is mounted in a single chip package (such as aplastic carrier, with leads that are affixed to a motherboard or otherhigher level carrier) or in a multichip package (such as a ceramiccarrier that has either or both surface interconnections or buriedinterconnections). In any case, the chip is then integrated with otherchips, discrete circuit elements, and/or other signal processing devicesas part of either (a) an intermediate product, such as a motherboard, or(b) an end product. The end product can be any product that includesintegrated circuit chips, ranging from toys and other low-endapplications to advanced computer products having a display, a keyboardor other input device, and a central processor.

It should also be understood that material compounds will be describedin terms of listed elements, e.g., SiGe. These compounds includedifferent proportions of the elements within the compound, e.g., SiGeincludes Si_(x)Ge_(1-x) where x is less than or equal to 1, etc. Inaddition, other elements can be included in the compound and stillfunction in accordance with the present principles. The compounds withadditional elements will be referred to herein as alloys.

Reference in the specification to “one embodiment” or “an embodiment”,as well as other variations thereof, means that a particular feature,structure, characteristic, and so forth described in connection with theembodiment is included in at least one embodiment. Thus, the appearancesof the phrase “in one embodiment” or “in an embodiment”, as well anyother variations, appearing in various places throughout thespecification are not necessarily all referring to the same embodiment.

It is to be appreciated that the use of any of the following “/”,“and/or”, and “at least one of”, for example, in the cases of “A/B”, “Aand/or B” and “at least one of A and B”, is intended to encompass theselection of the first listed option (A) only, or the selection of thesecond listed option (B) only, or the selection of both options (A andB). As a further example, in the cases of “A, B, and/or C” and “at leastone of A, B, and C”, such phrasing is intended to encompass theselection of the first listed option (A) only, or the selection of thesecond listed option (B) only, or the selection of the third listedoption (C) only, or the selection of the first and the second listedoptions (A and B) only, or the selection of the first and third listedoptions (A and C) only, or the selection of the second and third listedoptions (B and C) only, or the selection of all three options (A and Band C). This can be extended, as readily apparent by one of ordinaryskill in this and related arts, for as many items listed.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of exampleembodiments. As used herein, the singular forms “a,” “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises,” “comprising,” “includes” and/or “including,” when usedherein, specify the presence of stated features, integers, steps,operations, elements and/or components, but do not preclude the presenceor addition of one or more other features, integers, steps, operations,elements, components and/or groups thereof.

Spatially relative terms, such as “beneath,” “below,” “lower,” “above,”“upper,” and the like, can be used herein for ease of description todescribe one element's or feature's relationship to another element(s)or feature(s) as illustrated in the FIGS. It will be understood that thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the FIGS. For example, if the device in theFIGS. is turned over, elements described as “below” or “beneath” otherelements or features would then be oriented “above” the other elementsor features. Thus, the term “below” can encompass both an orientation ofabove and below. The device can be otherwise oriented (rotated 90degrees or at other orientations) and the spatially relative descriptorsused herein can be interpreted accordingly. In addition, it will also beunderstood that when a layer is referred to as being “between” twolayers, it can be the only layer between the two layers, or one or moreintervening layers can also be present.

It will be understood that when an element such as a layer, region orsubstrate is referred to as being “on” or “over” another element, it canbe directly on the other element or intervening elements can also bepresent. In contrast, when an element is referred to as being “directlyon” or “directly over” another element, there are no interveningelements present. It will also be understood that when an element isreferred to as being “connected” or “coupled” to another element, it canbe directly connected or coupled to the other element or interveningelements can be present. In contrast, when an element is referred to asbeing “directly connected” or “directly coupled” to another element,there are no intervening elements present.

It will also be understood that, although the terms first, second, etc.can be used herein to describe various elements, these elements shouldnot be limited by these terms. These terms are only used to distinguishone element from another element. Thus, a first element discussed belowcould be termed a second element without departing from the scope of thepresent concept. Having described preferred embodiments of a system andmethod (which are intended to be illustrative and not limiting), it isnoted that modifications and variations can be made by persons skilledin the art in light of the above teachings. It is therefore to beunderstood that changes may be made in the particular embodimentsdisclosed which are within the scope of the invention as outlined by theappended claims. Having thus described aspects of the invention, withthe details and particularity required by the patent laws, what isclaimed and desired protected by Letters Patent is set forth in theappended claims.

What is claimed is:
 1. A vertically stacked set of an n-type verticaltransport field effect transistor (n-type VT FET) and a p-type verticaltransport field effect transistor (p-type VT FET), comprising: a firstbottom source/drain layer on a substrate, wherein the first bottomsource/drain layer has a first conductivity type; a lower channel pillaron the first bottom source/drain layer; a first top source/drain on thelower channel pillar, wherein the first top source/drain has the firstconductivity type; a second bottom source/drain on the first topsource/drain, wherein the second bottom source/drain has a secondconductivity type different from the first conductivity type; an upperchannel pillar on the second bottom source/drain; and a second topsource/drain on the upper channel pillar, wherein the second topsource/drain has the second conductivity type different from the firstconductivity type.
 2. The vertically stacked set of the n-type VT FETand the p-type VT FET of claim 1, further comprising a bottomsource/drain extension region between the lower channel pillar and thefirst bottom source/drain layer.
 3. The vertically stacked set of then-type VT FET and the p-type VT FET of claim 1, wherein the first bottomsource/drain layer and first top source/drain are made of a materialselected from the group consisting of silicon and silicon-germanium. 4.The vertically stacked set of the n-type VT FET and the p-type VT FET ofclaim 1, wherein the second bottom source/drain layer and second topsource/drain are made of a material selected from the group consistingof silicon and carbon-doped silicon.
 5. The vertically stacked set ofthe n-type VT FET and the p-type VT FET of claim 1, wherein the lowerchannel pillar and upper channel pillar are undoped silicon.
 6. Thevertically stacked set of the n-type VT FET and the p-type VT FET ofclaim 1, further comprising a conductive strap of a metal silicide onthe first top source/drain and second bottom source/drain.
 7. Thevertically stacked set of the n-type VT FET and the p-type VT FET ofclaim 1, wherein the vertically stacked sets of channel pillars andsource/drains has a height in a range of about 80 nm to about 500 nm.